updated docs with iOS 10 compatible linking code

Summary:
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The current code for IOS contains deprecated code for incoming urls.
in iOS 10 deprecated openURL.
more details here: https://useyourloaf.com/blog/openurl-deprecated-in-ios10/

1. Create an RN app with iOS 10. set up linking as per instructions.

2. Using the iOS9 code snippet, with the app is open, navigate to the apps url scheme (in safari)  appname://value1/value2, the eventListener will not trigger.  note: it will however trigger getInitialURL if app is closed.

3. Replace the old iOS9 code with the iOS 10 and trigger an incoming url from a browser appname://
with the new code in the doc it will trigger for both open and closed apps.
Closes https://github.com/facebook/react-native/pull/13942

Differential Revision: D5071851

Pulled By: hramos

fbshipit-source-id: 8394de73014a1d2a5982b22b1b6fd09e0cf524dd

Libraries/Linking/Linking.js

@@ -66,12 +66,30 @@ const LinkingManager = Platform.OS === 'android' ?
  *   android:launchMode="singleTask">
  * ```
  *
- * NOTE: On iOS you'll need to link `RCTLinking` to your project by following
+ * NOTE: On iOS, you'll need to link `RCTLinking` to your project by following
  * the steps described [here](docs/linking-libraries-ios.html#manual-linking).
- * In case you also want to listen to incoming app links during your app's
+ * If you also want to listen to incoming app links during your app's
- * execution you'll need to add the following lines to your `*AppDelegate.m`:
+ * execution, you'll need to add the following lines to your `*AppDelegate.m`:
  *
  * ```
+ * // iOS 10
+ * #import <React/RCTLinkingManager.h>
+ * - (BOOL)application:(UIApplication *)application
+ *    openURL:(NSURL *)url
+ *    options:(NSDictionary<UIApplicationOpenURLOptionsKey,id> *)options
+ * {
+ *
+ *  return [RCTLinkingManager application:application openURL:url
+ *  sourceApplication:options[UIApplicationOpenURLOptionsSourceApplicationKey]
+ *             annotation:options[UIApplicationOpenURLOptionsAnnotationKey]];
+ *
+ * }
+ * ```
+ * 
+ * If you're targeting iOS 9 or older, you can use the following code instead:
+ *
+ * ```
+ * // iOS 9 or older
  * #import <React/RCTLinkingManager.h>
  *
  * - (BOOL)application:(UIApplication *)application openURL:(NSURL *)url
@@ -80,8 +98,12 @@ const LinkingManager = Platform.OS === 'android' ?
  *   return [RCTLinkingManager application:application openURL:url
  *          sourceApplication:sourceApplication annotation:annotation];
  * }
+ * ```
  * 
- * // Only if your app is using [Universal Links](https://developer.apple.com/library/prerelease/ios/documentation/General/Conceptual/AppSearch/UniversalLinks.html).
+ * If your app is using [Universal Links](https://developer.apple.com/library/prerelease/ios/documentation/General/Conceptual/AppSearch/UniversalLinks.html),
+ * you'll need to add the following code as well:
+ * 
+ * ```
  * - (BOOL)application:(UIApplication *)application continueUserActivity:(NSUserActivity *)userActivity
  *  restorationHandler:(void (^)(NSArray * _Nullable))restorationHandler
  * {